Despite constantly drawing Friday night's largest total audience, CBS cop drama 'Blue Bloods' is one of those shows that's almost an under the radar hit. It's barely ever the subject of "buzz" online or in the entertainment media, and it's never been either beloved or outright panned by critics. Yet 'Blue Bloods' has quietly spent three and a half years amassing a fiercely loyal fan following, to the point where the show is a total shoe-in for another renewal.

'Blue Bloods' stars Tom Selleck as NYPD commissioner Frank Reagan, whose sons Danny (Donnie Wahlberg) and Jamie (Will Estes) followed him into the family business and became police officers. Frank's daughter Erin (Bridget Moynahan) chose to fight crime in a different way, first becoming a prosecutor, then eventually earning the title of Executive Assistant District Attorney.

Which brings us to the fourth season 'Blue Bloods' installment set to air on Friday, Jan. 17. Entitled 'Unfinished Business,' the episode involves Erin reopening a cold murder case. Her search for answers brings her to a previously questioned witness to the crime, played by actor/comedian Doug E. Doug ('Cosby,' 'Law & Order: SVU'). The man in question won't exactly be hard to find, as he's currently behind bars, due to his suspected involvement in a different matter. Also appearing as a guest star will be Marion Ravenwood herself, Karen Allen . Indiana Jones' former main squeeze will be playing the distraught mother of the person that Doug's character saw get killed.